Method of operating a plunger lift system using a trip delay time in the afterflow time

ABSTRACT

A controller and method is provided for operating a plunger lift system in a gas well that uses a pressure trigger and trip delay time to determine an afterflow time. The plunger lift system can include a plunger and a valve between the well and an outlet line were the produced gas is routed. The method can open the valve and allow the plunger to rise to a top of the well. After the plunger has reached the top of the well, the pressure in the well can be monitored to determine when a pressure trigger has occurred. When the pressure trigger occurs, the method can wait a trip delay time before once again closing the valve. After a close time the method can be repeated, the valve opened and the plunger allowed to rise back up the well. An adjusted trip delay time can then be determined and used.

The invention relates to the control of an oil or gas well using a plunger lift system and more particularly to using a pressure trigger and a repeatedly adjusted trip delay time to determine an afterflow time.

BACKGROUND

A plunger lift is an artificial lift method that is used to remove fluids from a gas well. A plunger lift system uses a freely moving plunger in the production tubing. A seal is formed between the plunger and the production tubing that prevents fluid from passing between the plunger and the wall of the production tubing. The plunger is allowed to sit at the bottom of the well until sufficient pressure builds up behind the plunger and then the plunger is allowed to rise to the top of the well. Fluid that has accumulated on top of the plunger is carried up the well by the plunger to the well head, where this fluid is then removed from the well.

The movement of the plunger is controlled by opening and closing a valve between the production tubing and an outlet line (commonly called a sales line). When the valve is closed, the plunger drops to the bottom of the well. With the valve closed, the pressure from the well builds up and when a desired pressure level is reached, the valve can be opened, connecting the production tubing with the outlet line. Because the outlet line is typically at a lower pressure than the elevated pressure in the production tubing, the gas in the production tubing flows out of the well through the open valve and into the outlet line. This causes the plunger to rise in the well. When the plunger rises into the well head, it can then be held in the well head until the gas exiting the production well through the open valve is sufficiently reduced and the plunger can then fall back down the production tubing.

The time the plunger is held in the well head and the valve is left open is called the “afterflow” time. This afterflow time is the time that gas is being produced from the well by allowing it to leave the well and enter the outlet line. However, having too large of an afterflow time can cause too much water or other fluids to enter the well casing causing the well to “water in”. This can occur when the buildup of water in the well causes a hydrostatic barrier preventing gas from the formation from exiting the well. Over time, as more and more water is removed from the well casing by the plunger, the afterflow time may be able to be lengthened.

Typically, electronic controllers are used to control the operation of the plunger lift system. The electronic controller is used to control the opening and closing of the valve based on an afterflow time and a close time. Typically, these plunger lift systems will have a plunger arrival sensor positioned near the top of the well (usually in a plunger receiver in the well head) that can sense when the plunger has reached the top of the well.

Typically, the theory behind the operation of a plunger lift system is to try and have the plunger rising at a velocity that is not too slow to cause water and/or other fluids being carried above the plunger to fall off the top of the plunger, but not rising so fast that it breaks components and causes damage to the well head when it reaches the top of the well. The velocity of the plunger as it travels up the well when the valve to the outlet line is opened is determined by the length of the afterflow time. If the afterflow time used by the plunger lift system is too short, not enough water and/or other fluids will be allowed to build up in the well before the plunger is sent back down and the plunger will therefore rise too fast up the well. However, if the afterflow time is too long, too much fluid will build up in the well and the plunger's next trip up the well will be too slow or the excess fluid could even prevent the plunger from being able to rise back up the well when the valve is once again opened. Determining the proper afterflow time is one of the main factors in how well a plunger lift system will perform and there are numerous different ways an afterflow time can be determined in the prior art systems.

SUMMARY OF THE INVENTION

In a first aspect, a method of operating a plunger lift system in a gas producing well is provided. The method comprises: opening a control valve and allowing a plunger to rise to a top of the well; monitoring a pressure in the well while the valve is opened for a pressure trigger; when the pressure trigger occurs, waiting a trip delay time and after the trip delay time has passed closing the valve; after a close time has passed, opening the valve and allowing the plunger to rise to the top of the well; determining when the plunger has arrived at the top of the well; adjusting the trip delay time to determine an adjusted trip delay time based on the plungers arrival at the top of the well; and repeating the method using the adjusted trip delay time.

In another aspect, a plunger lift system for removing fluids from a well is provided. The system comprises: a wellhead provided at a top of the well and having a plunger receiver; production tubing connected to the well head and extending downwards down the well, the plunger receiver operatively connected to a top end of the production tubing; a plunger provided in the production tubing; an outlet line connected to the well head below the plunger receiver and fluidly connected with the production tubing; a control valve connected inline with the outlet line; a plunger sensor positioned on the outside of the plunger receiver to detect the plunger; a pressure sensor to detect a pressure in the well; and a controller operatively connected to the plunger sensor to receive information from the plunger sensor and the pressure sensor and operatively connected to the control valve to open and close the control valve. The controller is operative to perform a method comprising: opening a control valve and allowing the plunger to rise to a top of the well; using the pressure sensor, monitoring a pressure in the well while the valve is opened for a pressure trigger; when the pressure trigger occurs, waiting a trip delay time and after the trip delay time has passed closing the valve; after a close time has passed, opening the valve and allowing the plunger to rise to the top of the well; determining when the plunger has arrived at the top of the well; adjusting the trip delay time to determine an adjusted trip delay time based on the plungers arrival at the top of the well; and repeating the method using the adjusted trip delay time.

In a further aspect, a controller for controlling the operation of a plunger lift system for a gas producing well having a plunger, a plunger sensor, a pressure sensor and a valve between the well and an outlet line is provided. The controller comprises: a processing unit; an input interface operatively connectable to the plunger sensor and the pressure sensor; an output interface operatively connectable to the valve and operative to open and close the valve; and a memory containing program instructions. The processing unit responsive to the program instructions and operative to perform a method comprising: opening a control valve and allowing the plunger to rise to a top of the well; using the pressure sensor, monitoring a pressure in the well while the valve is opened for a pressure trigger; when the pressure trigger occurs, waiting a trip delay time and after the trip delay time has passed, closing the valve; after a close time has passed, opening the valve and allowing the plunger to rise to the top of the well; determining when the plunger has arrived at the top of the well; adjusting the trip delay time to determine an adjusted trip delay time based on the plungers arrival at the top of the well; and repeating the method using the adjusted trip delay time.

DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the present invention is described below with reference to the accompanying drawings, in which:

FIG. 1 illustrates a plunger lift system;

FIG. 2 is a state diagram showing the two modes of operation of the plunger lift system;

FIG. 3 is a schematic illustration of a controller used in the plunger lift system;

FIG. 4 is a graph illustrating how the pressure inside the well casing varies during the operation of the plunger lift system; and

FIG. 5 illustrates a flowchart of a method of operating a plunger lift system using a pressure trigger and a repeatedly adjusted trip delay time.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

FIG. 1 illustrates a plunger lift system 10 for removing fluids from a well 100. The plunger lift system 10 can include: a wellhead 20: a plunger 30; production tubing 40; a controller 50; an outlet line 60; a control valve 70; a plunger sensor 80; a discharge line 90; and other equipment for the operation of the plunger lift system 10.

The well 100 is typically provided with a well casing 110. Production tubing 40 can be provided running down the well casing 110 between the wellhead 20 and the bottom 42 of the production tubing 40.

The plunger 30 can be provided in the production tubing 40 so that the plunger 30 is able to move up and down in the production tubing 40. The plunger 30 can form a seal with the wall 46 of the production tubing 40 to prevent significant amounts of fluids from passing around the plunger 30 between the outside of the plunger 30 and the wall 46 of the production tubing 40.

The wellhead 20 can be provided at a top of the well casing 110 and the production tubing 40. The wellhead 20 can fluidly connect the production tubing 40 and the well casing 110 to the outlet line 60. The outlet line 60 routes gas out of the well 100 for transport or collection. A control valve 70 can be provided between the outlet line 60 and the well 100.

The wellhead 20 can include a plunger receiver 22 operatively connected to a top end 44 of the production tubing 40 and above where the outlet line 60 is connected. At the top of its travel, the plunger 30 can enter the plunger receiver 22 and be held in place in the plunger receiver 22 entirely above where the outlet line 60 connects with the well 100. Alternatively, the plunger receiver 22 can be configured so that the pressure of the gas being produced from the well 100 will hold the plunger 30 at the top of the well 100 and in the plunger receiver 22 with the plunger 30 just bouncing at the top of the well 100, rather than the plunger 30 being physically held in the plunger receiver 22.

A plunger sensor 80 can be positioned relative to the plunger receiver 22 so that the plunger 30 will pass by the plunger sensor 80 when the plunger 30 enters the plunger receiver 22. This plunger sensor 80 could be a typical arrival sensor that is able to sense when the plunger 30 passes by the sensor 80 or it could be a velocity sensor capable of measuring the velocity of the plunger 30 as it passes by the plunger sensor 80.

A pressure sensor 82 can also be used that measures the pressure in the well casing 110.

A discharge line 90 can be connected to the plunger receiver 22 so that fluids pushed into the plunger receiver 22 by the plunger 30 can be removed from the plunger receiver 22. In some cases, these fluids may be routed through a separator (not shown) so that unwanted liquids and other contaminants can be removed from the plunger receiver 22. If the plunger lift system 10 is being used to produce oil (or other saleable liquids) from the well 100, the oil is discharged out of the plunger lift system 10 through this discharge line 90. Alternatively, the plunger receiver 22 can have a number of different configurations for receiving the plunger 30 and removing fluid from the top of the plunger 30.

Referring to FIG. 2, the plunger lift system 10 can alternate between an open cycle 201 (or production cycle) where the control valve 70 is opened and gas is flowing out of the well 100 through the outlet line 60 and a closed cycle 203 (or shut in cycle) where the control valve 70 is closed and gas is prevented from flowing out of the well 100 into the outlet line 60 allowing the pressure in the well 100 to increase. A first trigger 205 will cause the plunger lift system 10 to change from operating in the open cycle 201 to operating in the closed cycle 203 and a second trigger 207 will cause it to move from the closed cycle 203 to the open cycle 201. Typically, this first trigger 205 is the closing of the valve 70 and the second trigger 207 is an opening of the valve 70.

During the closed cycle 203, when the control valve 70 is closed and gas cannot flow out of the well 100 to the outlet line 60, the plunger 30 can drop down the well 100 to a position proximate the bottom of the well 100. When the closed cycle 203 is finished and the control valve 70 is opened, pressure that has built up in the well 100 causes the plunger 30 to rise up the production tubing 40 to the wellhead 20 and into the plunger receiver 22. Once the plunger 30 is in place in the plunger receiver 22, the control valve 70 can remain open and gas can be produced from the well 100 by allowing it to flow into the outlet line 60. Any fluid brought up the well 100 above the plunger 30 can be discharged out the discharge line 90. The time the control valve 70 is opened is the open cycle 201.

Once the open cycle ends 201 and the control valve 70 is closed, the plunger 30 can be released by the plunger receiver 22 and the weight of the plunger 30 can cause it to drop back down the production tubing 40 to the bottom of the well 100. As the closed cycle 203 continues and the control valve 70 remains closed, the pressure in the well 100 can increase. When the pressure has increased to a sufficient level, the control valve 70 can once again be opened and the open cycle 201 can begin and the plunger 30 can begin to rise to the top of the well 100.

When the plunger lift system 10 is used to produce gas from the well 100, it is desirable to maximize the time the plunger lift system 10 remains in the open cycle 201 so that as much time as possible is spent producing gas from the well 100 during this open cycle 201, but not have the open cycle 201 occur for so long that the well 100 waters in and the well 100 stops flowing gas because the weight of water in the well 100 and the plunger 30 is too great for the pressure of the gas below the plunger 30 to lift the plunger 30 up the well 100.

FIG. 3 illustrates a controller 50 that can be used to control the operation of the plunger lift system 10 and alter the operation of the plunger lift system 10 between the open cycle and the closed cycle. Referring again to FIG. 1, the controller 50 can be operably connected to the solenoid 72 so that by sending signals to the solenoid 72 the controller 50 can cause the opening and closing of the control valve 70. The controller 50 can also be operatively connected to the plunger sensor 80 so that the controller 50 can receive output from the plunger sensor 80 that the controller 50 can then use to approximate the speed of the plunger 30 as it passes the plunger sensor 80.

Referring again to FIG. 3, the controller 50 can include a processing unit 302, such a microprocessor that is operatively connected to a computer readable memory 304 and can control the operation of the controller 50. Program instructions for controlling the operation of the processing unit 302 can be stored in the memory 304 as well as any additional data needed for the operation of the controller 50. A keypad 306 and a display 303 can be provided to allow a user to see the settings of the controller 50 and enter inputs and change parameters of the controller 50. An input interface 320 can be provided operatively connected to the processing unit 302 so that the controller 50 can receive signals from external sensors. The sensor 80 can be connected to the input interface 320 to allow signals from the sensor 80 to be transmitted to the controller 50. The pressure sensor 82 sensing the pressure in the well casing 110 and other portions of the well can also be connected to the input interface 320. An output interface 322 can be provided operatively connected to the processing unit 302 to send signals to other devices in the plunger lift system 10. For example, the solenoid 72 attached to the control valve 70 can be connected to the output interface 322 so that the controller 50 can send signals to the solenoid 72.

Because the controller 50 is frequently used in a remote location because the well 100 the controller 50 is being used with is located in a remote location, the controller 50 can be connected to a solar panel 310 that supplies power to controller 50. A battery 314 can be provided to power the processing unit 302 and the battery 314 can be charged with a battery charger 312 connected to the solar panel 310. A voltage regulator 316 can be provided between the processing unit 302 and the battery 314 to provide the proper voltage to the processing unit 302.

The controller 50 can include a weatherproof enclosure for protecting the components of the controller 50 from the elements.

When the plunger lift system 10 is used to produce gas from the well 100, ideally the length of the afterflow is maximized without this afterflow time being so long that the well 100 will water in during this afterflow time. At the same time, the close time can be minimized, simply providing enough time for the plunger 30 to reach the bottom of the well 100 and collect the water that has collected there before the valve 70 is once again opened and the plunger 30 is used to carry the water to the top of the well 100 and gas is once more being produced from the well 100.

FIG. 4 illustrates a graph of the typical changes of the pressure in the well casing 110 as the plunger lift system 10 is in operation. When the control valve 70 is opened at point A, the pressure in the well casing 110 can increase as the plunger 30 rises in the well 100 until the plunger 30 reaches the plunger receiver 22 at the top of the well 100. Once the plunger 30 has reached the plunger receiver 22 at point B, the plunger 30 can be held in the plunger receiver 22 while the control valve 70 remains open and gas is produced from the well 100 through the outlet line 60. This is the afterflow time which occurs between points B and C on the graph. During the afterflow time, as the control valve 70 remains in the open position, the pressure in the well casing 110 will decrease relatively rapidly at first. As the pressure in the well casing 110 is bled off through the outlet line 60, the rate of the decrease in the casing pressure will start to slow down before it reaches a minimum pressure, X, before the pressure in the well casing 110 once again starts to increase at a much slower rate as fluids begin to build up in the well casing 110.

Once the control valve 70 is once again closed after the afterflow time at point C, the pressure in the well casing 110 will build more rapidly as the gas entering the well casing 110 is prevented from flowing out of the well 100 into the outlet line 60. The plunger 30 will also be dropped back down the production tubing 40 in the well 100 after the control valve 60 is closed.

When the close time is over at point D, the control valve 70 will be opened and the plunger 30 will once again rise up the well, starting the cycle all over again.

When the plunger lift system 10 is used to produce gas from the well 100, it is desirable to maximize the afterflow time (shown between points B and C on FIG. 4) so that as much time as possible is spent producing gas from the well 100 before the control valve 70 is once again closed at point C and the production of gas is temporarily stopped while pressure is once again allowed to build up in the well casing 110. However, as you can see in the afterflow time between points B and C the casing pressure will drop to a low pressure point X where the slope of the line is 0. This will be the point where the pressure in the well casing 110 is at its lowest. After this point, the pressure in the well casing 110 will increase slightly over time above this lowest point X. This increase in the pressure in the well casing 110 after its lowest point X is a result of fluid once again starting to build up in the well casing 110. The fluid that is allowed to build up in the well 100 will be carried back up the well 100 on top of the plunger 30 when the plunger 30 is brought back up the well 100 when the control valve 70 is closed. The amount of fluid being carried on top of the plunger 30 will determine the speed of the plunger 30 as it travels back up the well 100. With little fluid on top of the plunger 30, the plunger 30 will travel fast up the well 100. With more fluid on top of the plunger 30, the plunger 30 will travel slower up the well 100 because it has to carry more fluid on top of it. By carrying the proper amount of fluid on top of the plunger 30 a safe velocity of the plunger 30 can be achieved. The fluid on top of the plunger 30 can also cushion the impact of the plunger 30 in the plunger receiver 22 when it reaches the top of the well 100 and prevent damage to the surface equipment. Having some fluid built up in the well 100 when the plunger 30 is dropped back down the well 100 can also prevent damage to the bottom hole assembly because this fluid in the bottom of the well 100 can serve to cushion the plunger 30 when it reaches the bottom of the well 100, preventing violent impacts of the plunger 30 in the bottom of the well 100. The amount of fluid that collects in the bottom of the well 100 before the plunger 30 is sent back down the well 100 is determined by the length of the afterflow time. If the afterflow time used is too long, too much fluid can build up in the well casing 110 before the control valve 70 is closed and the plunger 30 is sent back down the well 100 and there will be too much fluid on top of the plunger 30 when it makes the trip back up the well 100. This can slow down the speed of the plunger 30 when it travels back up the well 100 and it can even make it hard to bring the plunger 30 back up the well 100. Eventually, if too much fluid is allowed to build up in the well 100 because the afterflow time is much longer than it should be, the fluid on top of the plunger 30 can make it too heavy to get the plunger 30 back up the well 100 to the surface and a swabbing truck will have to be used to remove the fluid from the well 100 so the plunger lift system 10 can once again operate.

On the other hand, if the afterflow time used is too short, when the control valve 70 is closed after the afterflow time and the plunger 30 is sent back down the well 100 then production of gas out the outlet line 60 will be stopped prematurely and not all of the gas that could be obtained will be. Additionally, there will be less fluid that has collected in the well 100 and therefore there will be less fluid on top of the plunger 30 when it travels back up the well 100. This smaller amount of fluid can cause the plunger 30 to travel back up the well 100 too fast and reach the plunger receiver 22 traveling at a speed that can damage the plunger receiver 22.

FIG. 5 illustrates a flowchart of a method for determining an afterflow time based on sensing a pressure trigger in the pressure in the well casing 110 and then waiting a trip delay time after the pressure trigger has occurred before closing the control valve 70 to shut in the well 100 and sending the plunger 30 back down the well 100. However, either or both of the pressure trigger and trip delay time may be input into the controller 50 by an operator which means that the operator must use his or her best judgment in setting these parameters thereby introducing human error into the method. Failure to be exactly right in setting either one or both of these parameters can result in the plunger lift system 20 operating in a less than ideal manner and using an afterflow time that is less ideal than it could be. Therefore, the current method will evaluate the trip of the plunger 30 after each trip up the well 100 and can adjust the trip delay time used by the method to try and optimize the afterflow time and therefore the operation of the plunger lift system 20. By evaluating each trip of the well 100 by the plunger 30 and then adjusting the trip delay time accordingly, the method can fine tune the trip delay time each time with the goal of bringing the plunger 30 to the surface next time at the desired velocity or closer to the desired velocity.

Referring again to FIG. 4, a pressure trigger that is a rate of change of the casing pressure (or a specific slope of the line indicating the casing pressure in graph) and the trip delay time making up the afterflow time are shown that can be used in the method shown in the flowchart of FIG. 5. In the method, after point B with the plunger 30 having reached the plunger receiver 22 at the top of the well 100, the pressure in the well casing 110 can be monitored as it decreases after point B. When the pressure decreases to the pressure trigger, the method will then delay for a trip delay time before point C is reached with the control valve 70 being shut and the plunger 30 allowed to drop back down the well 100.

The pressure trigger that causes the method to start the trip delay time could be a number of things. In one aspect, the pressure trigger could be a rate of change threshold for the pressure in the well casing 110 (the slope of the casing pressure line on the graph). Because the pressure in the well casing 110 will initially decrease at a relatively rapid rate, the rate of change of the pressure in the well casing 110 will be relatively large and because the pressure is decreasing it will be a negative value. However, as the pressure in the well casing 110 begins to reach its lowest point X, the pressure decreases at a more gradual rate and this rate of change will become a smaller and smaller negative value. This rate of change will eventually become 0 at the lowest pressure point X before the pressure in the well casing 110 once again begins to build as a result of fluid from the surrounding formation entering the well 100. After the lowest pressure point X, the rate of change will become a positive value as the pressure in the well casing 110 continues to increase until point C at the end of the afterflow time and the control valve 70 is closed.

By using a relatively small, negative value, the pressure trigger can be set to occur before the lowest pressure point X, by using 0 for the rate of change, the pressure trigger can be set to occur at the lowest pressure point X and by using a relatively small, positive value, the pressure trigger can be set to occur after the lowest pressure point X.

In one aspect, the rate of change threshold can be specified by a user. The user would choose what this rate of change threshold would be and enter it into the controller 50. Alternatively, the controller 50 can use a pre-defined threshold such as a small negative value or small positive value to indicate the slowing or increasing of the casing pressure rate of change. In a further aspect, the rate of change threshold could be set to a 0 value which would correspond with the casing pressure reaching its minimum point before it starts to increase again.

The trip delay time can be a period of time that is set to try and cause point C (the end of the afterflow time) to occur at an optimal time when just enough fluid has entered the well 100 before the well 100 is shut in by closing the control valve 70 and the plunger is dropped back down the well 100. This trip delay time could be specified by the user or pre-set in the controller.

Referring again to FIG. 5, the method can start and at step 502 the pressure trigger and the initial time delay can be obtained by the controller 50. This pressure trigger can either be set by the operator or alternatively it could be pre-set in the controller 50 and unalterable by an operator using the controller 50. If the pressure trigger is predefined in the controller 50 and not alterable by an operator, this could take one more parameter out of the operator's hands allowing him or her very limited control over the settings in the controller 50 and reducing or even eliminating human judgment and therefore human error.

The initial time delay could also either be set by the operator or be a pre-determined time period used by the controller 50. Typically, the operator will be allowed to set at least one of either the pressure trigger and the initial time delay, which the operator will set based on his or her judgment of the operation of the plunger lift system 10.

The method will move to step 504 and open the control valve 70 to allow the plunger lift system 10 to start producing gas from the well 100. This will be point B on the graph shown in FIG. 4. After the valve is opened at step 504, the method will move on to step 506 and the controller 50 will start monitoring the pressure in the well casing 110 to determine when the pressure trigger occurs at step 508. This can be done by the controller 50 using a pressure sensor 82 to monitor the pressure in the well casing 110 over time. If this pressure trigger is a rate of change of the casing pressure, step 508 will occur when the controller 50 determines this rate of change of the casing pressure has occurred.

When the controller 50 determines the pressure trigger has occurred at step 508, the method will move on to step 510 and wait for the trip delay time to pass before moving on to step 512 and closing the control valve 70 to shut in the well 100 and dropping the plunger 30 back down the well 100. The trip delay time used the first time will be the initial trip delay time obtained at step 502. Step 512 will correspond with point C on the graph shown in FIG. 4 and is the shutting in of the well 100.

The method will then move to step 514 and enter a close delay time where the controller 50 is simply allowing the casing pressure in the in the well 100 to build up high enough to force the plunger 30 up the well 100 when the control valve 70 is reopened at step 516.

Alternatively, instead of delaying for a period of time (or the close time) at step 514, the method could also wait until a desired pressure differential between the pressure in the well casing 110 and the pressure in the outlet line 60 is reached, a desired pressure differential between the pressure in the pressure in the production tubing 40 and the pressure in the outlet line 60 is reached or a desired load factor is achieved. The load factor could be achieved by taking the difference between the pressure in the well casing 110 and the pressure in the production tubing 40 and dividing it by the difference between the pressure in the well casing 110 and the pressure in the outlet line 60.

After step 514 is completed, the method will move on to step 516 and open the control valve 70 to cause the plunger 30 to rise up the well 100. Step 516 will correspond with point A on the graph shown in FIG. 4.

After step 516, the controller 50 will wait for the plunger sensor 80 to sense that the plunger 30 has arrived in the plunger receiver 22 at step 518 and the method will then move onto step 520 and adjust the trip delay time. Simply setting a pressure trigger and a trip delay time at the beginning of the operation of the plunger lift system 10 and then using these same parameters throughout the operation of the plunger lift system 10 is very unlikely to achieve optimal performance of the plunger lift system 10 and may not even achieve decent performance of the plunger lift system 10. If these values are preset in the controller 50, it is unlikely these preset values will be ideal for a particular well 100 the plunger lift system 10 is being used in. If an operator is allowed to choose the pressure trigger and/or the trip delay time, this will make the performance of the plunger lift system 10 dependent upon the user's judgment regarding what he or she thinks might be an ideal pressure trigger and/or trip delay time. This introduces the requirement to rely on human judgment and introduces the potential for human error. Additionally, even if the pressure trigger and/or initial trip delay time chosen by an operator happen to be nearly ideal for a particular well 100, over time the conditions in the well 100 can change and the afterflow time achieved by the pressure trigger and initial trip delay time can cause the plunger lift system 10 to operate less effectively than it otherwise could.

By evaluating the trip of the plunger 30 up the well 100 after it reaches the top of the well 100 (point B of the graph shown in FIG. 4), the trip delay time can be adjusted for the next cycle of the plunger lift system 10 to try and improve the overall performance of the plunger lift system 10. The trip of the plunger 30 up the well 100 can be evaluated by a number of different factors. If the plunger sensor 80 is a typical arrival sensor that can simply measure the arrival of the plunger 30 at the top of the well 100, the time it took the plunger 20 to rise to the top of the well 100 from the bottom of the well 100 (the “trip time”) can be evaluated. Additionally, using the depth of the well 100 and this trip time the average velocity of the plunger 30 as it rises up the well 100 can be determined. Alternatively, if the plunger sensor 80 is a velocity sensor capable of measuring the velocity of the plunger 30 as it reaches the top of the well 100, this velocity of the plunger 30 can be used to evaluate the trip of the plunger 30 up the well 100. This evaluation of the trip of the plunger 30 up the well 100 can then be used to adjust the trip time delay and try to optimize it to improve the performance of the plunger lift system.

In one aspect, if the plunger sensor 80 is an arrival sensor that can simply determine when the plunger 30 has arrived in the plunger receiver 22, at step 520 the controller 50 may use a difference between a maximum afterflow time and a minimum afterflow time to make adjustments to the trip delay time. This adjustment to the trip delay time could be determines as follows:

${\Delta \; {TripDelayTime}} = {\frac{{TargetRise} - {ActualRise}}{TargetRise} \times {ScalingFactor} \times \left\lbrack {{{Max}\; {AF}} - {{Min}\; {AF}}} \right\rbrack}$

where ΔTripDelayTime is the change to be made to the trip delay time, TargetRise is the target rise time or ideal rise time the plunger 30 should take to travel from the bottom of the well 100 to the top of the well 100, ActualRise is the actual time it takes the plunger 30 to travel from the bottom of the well 100 to the top of the well, ScalingFactor is a range between 0 and 1 that allows an operator to set how aggressive a change is to be made to trip delay time, the MaxAF will be the maximum afterflow time that is desired for the well 100 and the MinAF will be the minimum afterflow time that is desired for the well. The MaxAF and MinAF will set limits on the afterflow time that can be used by the plunger lift system 10.

Because the difference between the maximum afterflow and the minimum afterflow could be quite large, the adjustment to the trip delay time could be quite large as well if the ScalingFactor is 1 or close to 1. Therefore, in some case it may be desirable to have this scaling factor set to a lower value, such as between 0.01 and 0.15, to prevent the trip delay time from being increased or decreased by too large an amount at any one time.

In another aspect, if the plunger sensor 80 is a arrival sensor that can simply determine when the plunger 30 has arrived in the plunger receiver 22, at step 520 the controller 50 could also use the current trip delay time to determine the adjustment to the trip delay time as follows:

${\Delta \; {TripDelayTime}} = {\frac{{TargetRise} - {ActualRise}}{TargetRise} \times {ScalingFactor} \times {CurrentTripDelayTime}}$

where ΔTripDelayTime is the change to be made to the trip delay time, TargetRise is the target rise time or ideal rise time the plunger 30 should take to travel from the bottom of the well 100 to the top of the well 100, ActualRise is the actual time it takes the plunger 30 to travel from the bottom of the well 100 to the top of the well, ScalingFactor is a range between 0 and 1 that allows an operator to set how aggressive a change is to be made to trip delay time, and CurrentTripDelayTime will be the current trip delay time.

Alternatively, if the plunger sensor 80 is capable of measuring the velocity of the plunger 30 as the plunger 30 arrives at the top of the well 100, the velocity measurement could be used to determine an adjustment to the trip delay time. If this is the case, by pre-defining the pressure trigger in the controller 50 and not letting an operator set the pressure trigger, the only parameter the operator needs to be concerned with is the safe surface velocity of the plunger 30 when it arrives at the top of the well 100. The controller 50 would only need this velocity of the plunger 30 to then alter the trip delay time if necessary and adjusting the trip delay time using the surface velocity of the plunger 30 will adjust the amount of fluid that is being brought to surface to give us the desired surface velocity of the plunger 30. For example, the surface velocity could be used with the following equation to determine an adjustment to the trip delay time:

${\Delta \; {TripDelayTime}} = {\frac{{ActualVelocity} - {TargetVelocity}}{TargetVelocity} \times {ScalingFactor} \times {CurrentTripDelayTime}}$

where ΔTripDelayTime is the change to be made to the trip delay time, TargetVelocity is the target velocity or ideal velocity the plunger 30 should be traveling at when it reaches the top of the well 100, ActualVelocity is the actual, measured velocity of the plunger 30 at the top of the well 100 as measured by the plunger sensor 80 and determined at step 407, ScalingFactor is a range between 0 and 1 that allows an operator to set how aggressive a change is to be made to trip delay time and the CurrentTripDelayTime is the current trip delay.

In further aspects, other things about the trip of the plunger 30 could be used to adjust the trip delay time, for example, the velocity of the plunger 30 at any point in its trip of the well 100 could be used, the kinetic energy of the plunger 30 at any point in its trip of the well 100, the impact force of the plunger 30 in the plunger receiver 22, etc.

Once an adjustment to the trip delay time has been determined, the controller 50 can then vary the initial trip delay time by the determined adjustment to result in an adjusted trip delay time as follows:

AdjustedTripDelayTime=CurrentTripDelayTime+ΔTripDelayTime

With this adjusted trip delay time, step 520 can end and the method can return to step 504 and once again open the control valve 70 to once again start producing gas from the well 100 and monitoring the pressure in the well casing 110 at step 506 to determine when the pressure trigger will occur in the well casing 110. When the pressure trigger occurs at step 508, the method will move onto step 510 and wait for the trip delay time that was determined previously at step 520.

After this new trip delay time has passed, the method will repeat step 512 where it will close the control valve 70 and drop the plunger 30 back down the well, step 514 where it will delay a close time, step 516 where it will open the control valve 70 to allow the plunger 30 to rise to the top of the well 100 again and sense its arrival in the plunger receiver 22 at step 518. It can then evaluate the plunger 30 most recent trip up the well and once again determine an adjustment to the trip delay time at step 520 before returning to step 504 and repeating the method.

By evaluating the trip of the plunger 30 up the well 100 after each trip up the well 100 and adjusting the trip delay time as necessary, the method can try and optimize the afterflow time to improve the performance of the plunger lift system 10. Additionally, if an operator is allowed to set the pressure trigger and/or the trip delay time and makes a mistake or even decides on less than ideal values for these parameters, the method can automatically correct for these errors by adjusting the trip delay time (over several cycles if necessary), reducing the impact of operator error.

The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous changes and modifications will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all such suitable changes or modifications in structure or operation which may be resorted to are intended to fall within the scope of the claimed invention. 

1. A method of operating a plunger lift system in a well, the method comprising: opening a control valve and allowing a plunger to rise to a top of the well; monitoring a pressure in the well while the valve is opened for a pressure trigger; when the pressure trigger occurs, waiting a trip delay time and after the trip delay time has passed closing the valve; after a close time has passed, opening the valve and allowing the plunger to rise to the top of the well; determining when the plunger has arrived at the top of the well; adjusting the trip delay time to determine an adjusted trip delay time based on the plungers arrival at the top of the well; and repeating the method using the adjusted trip delay time.
 2. The method of claim 1 wherein the pressure trigger is a rate of change of pressure in the well over time.
 3. The method of claim 2 wherein the pressure trigger is a positive value.
 4. The method of claim 2 wherein the pressure trigger is a negative value.
 5. The method of claim 2 wherein the pressure trigger is a value of zero.
 6. The method of claim 1 wherein the method determines a rise time of the time the plunger took to travel up the well and the adjusted trip delay time is determined based on the rise time.
 7. The method of claim 6 wherein the adjusted trip delay is based on a difference between the rise time of the plunger and a target rise time for the plunger to rise up the well.
 8. The method of claim 6 wherein the adjusted trip delay time is determined using the function: ${\Delta \; {TripDelayTime}} = {\frac{{TargetRise} - {ActualRise}}{TargetRise} \times {ScalingFactor} \times \left\lbrack {{{Max}\; {AF}} - {{Min}\; {AF}}} \right\rbrack}$   and AdjustedTripDelayTime = CurrentTripDelayTime + Δ TripDelayTime and wherein, ΔTripDelayTime is the change to be made to the trip delay time, TargetRise is the target rise time of the plunger to travel to the top of the well, ActualRise is the actual time it took the plunger to travel to the top of the well, ScalingFactor is a value between 0-1, MaxAF is a maximum afterflow time, and and MinAF is a the minimum afterflow time.
 9. The method of claim 8 wherein the ScalingFactor is
 1. 10. The method of claim 6 wherein the adjusted trip delay time is determined using the function: ${\Delta \; {TripDelayTime}} = {\frac{{TargetRise} - {ActualRise}}{TargetRise} \times {ScalingFactor} \times {CurrentTripDelayTime}}$   and AdjustedTripDelayTime = CurrentTripDelayTime + Δ TripDelayTime and wherein, ΔTripDelayTime is the change to be made to the trip delay time, TargetRise is the target rise time of the plunger to travel to the top of the well, ActualRise is the actual time it took the plunger to travel to the top of the well, ScalingFactor is a value from 0-1, and CurrentTripDelayTime is the a current trip delay time.
 11. The method of claim 10 wherein the ScalingFactor is
 1. 12. The method of claim 1 wherein a velocity of the plunger is determined and the determined velocity is used to determine the adjusted trip delay time.
 13. The method of claim 12 wherein the adjusted trip delay is based on a difference between the determined velocity of the plunger and a target velocity of the plunger.
 14. The method of claim 12 where the determined velocity is of a velocity of the plunger at a top of the well.
 15. The method of claim 12 wherein the adjusted trip delay time is determined using the function: ${\Delta \; {TripDelayTime}} = {\frac{{ActualVelocity} - {TargetVelocity}}{TargetVelocity} \times {ScalingFactor} \times {CurrentTripDelayTime}}$   and AdjustedTripDelayTime = CurrentTripDelayTime + Δ TripDelayTime
 16. A plunger lift system for removing fluids from a well, the system comprising: a wellhead provided at a top of the well and having a plunger receiver; production tubing connected to the well head and extending downwards down the well, the plunger receiver operatively connected to a top end of the production tubing; a plunger provided in the production tubing; an outlet line connected to the well head below the plunger receiver and fluidly connected with the production tubing; a control valve connected inline with the outlet line; a plunger sensor positioned on the outside of the plunger receiver to detect the plunger; a pressure sensor to detect a pressure in the well; and a controller operatively connected to the plunger sensor to receive information from the plunger sensor and the pressure sensor and operatively connected to the control valve to open and close the control valve, the controller operative to perform a method comprising: opening a control valve and allowing the plunger to rise to a top of the well; using the pressure sensor, monitoring a pressure in the well while the valve is opened for a pressure trigger; when the pressure trigger occurs, waiting a trip delay time and after the trip delay time has passed closing the valve; after a close time has passed, opening the valve and allowing the plunger to rise to the top of the well; determining when the plunger has arrived at the top of the well; adjusting the trip delay time to determine an adjusted trip delay time based on the plungers arrival at the top of the well; and repeating the method using the adjusted trip delay time.
 17. The plunger lift system of claim 16 wherein the pressure trigger is a rate of change of pressure in the well over time.
 18. The plunger lift system of claim 16 wherein the controller determines a rise time of the time the plunger to travel up the well and the adjusted trip delay time is determined based on the rise time.
 19. The plunger lift system of claim 18 wherein the adjusted trip delay is based on a difference between the rise time of the plunger and a target rise time for the plunger to rise up the well.
 20. The plunger lift system of claim 16 wherein a velocity of the plunger is determined and the determined velocity is used to determine the adjusted trip delay time.
 21. The plunger lift system of claim 20 wherein the adjusted trip delay is based on a difference between the determined velocity of the plunger and a target velocity of the plunger.
 22. The plunger lift system of claim 20 where the determined velocity is of a velocity of the plunger at a top of the well.
 23. A controller for controlling the operation of a plunger lift system for a well having a plunger, a plunger sensor, a pressure sensor and a control valve between the well and an outlet line, the controller comprising: at least one processing unit; an input interface operatively connectable to the plunger sensor and the pressure sensor; an output interface operatively connectable to the valve and operative to open and close the valve; and at least one memory containing program instructions, the at least one processing unit responsive to the program instructions and operative to perform a method comprising: opening a control valve and allowing the plunger to rise to a top of the well; using the pressure sensor, monitoring a pressure in the well while the valve is opened for a pressure trigger; when the pressure trigger occurs, waiting a trip delay time and after the trip delay time has passed, closing the valve; after a close time has passed, opening the valve and allowing the plunger to rise to the top of the well; determining when the plunger has arrived at the top of the well; adjusting the trip delay time to determine an adjusted trip delay time based on the plungers arrival at the top of the well; and repeating the method using the adjusted trip delay time.
 24. The controller of claim 23 wherein an operator can set only one of: the pressure trigger; and the trip delay time.
 25. The controller of claim 23 wherein the pressure trigger is a rate of change of pressure in the well over time.
 26. The controller of claim 25 wherein the pressure trigger is a positive value.
 27. The controller of claim 25 wherein the pressure trigger is a negative value.
 28. The controller of claim 25 wherein the pressure trigger is a value of zero.
 29. The controller of claim 23 wherein the controller determines a rise time of the time the plunger to travel up the well and the adjusted trip delay time is determined based on the rise time.
 30. The controller of claim 29 wherein the adjusted trip delay is based on a difference between the rise time of the plunger and a target rise time for the plunger to rise up the well.
 31. The controller of claim 29 wherein the adjusted trip delay time is determined using the function: ${\Delta \; {TripDelayTime}} = {\frac{{TargetRise} - {ActualRise}}{TargetRise} \times {ScalingFactor} \times \left\lbrack {{{Max}\; {AF}} - {{Min}\; {AF}}} \right\rbrack}$   and AdjustedTripDelayTime = CurrentTripDelayTime + Δ TripDelayTime and wherein, ΔTripDelayTime is the change to be made to the trip delay time, TargetRise is the target rise time of the plunger to travel to the top of the well, ActualRise is the actual time it took the plunger to travel to the top of the well, ScalingFactor is a value between 0-1, MaxAF is a maximum afterflow time, and and MinAF is a the minimum afterflow time.
 32. The controller of claim 31 wherein the ScalingFactor is
 1. 33. The controller of claim 29 wherein the adjusted trip delay time is determined using the function: ${\Delta \; {TripDelayTime}} = {\frac{{TargetRise} - {ActualRise}}{TargetRise} \times {ScalingFactor} \times {CurrentTripDelayTime}}$   and AdjustedTripDelayTime = CurrentTripDelayTime + Δ TripDelayTime and wherein, ΔTripDelayTime is the change to be made to the trip delay time, TargetRise is the target rise time of the plunger to travel to the top of the well, ActualRise is the actual time it took the plunger to travel to the top of the well, ScalingFactor is a value from 0-1, and CurrentTripDelayTime is the a current trip delay time.
 34. The controller of claim 33 wherein the ScalingFactor is
 1. 35. The controller of claim 23 wherein a velocity of the plunger is determined and the determined velocity is used to determine the adjusted trip delay time.
 36. The controller of claim 35 wherein the adjusted trip delay is based on a difference between the determined velocity of the plunger and a target velocity of the plunger.
 37. The controller of claim 35 where the determined velocity is of a velocity of the plunger at a top of the well.
 38. The controller of claim 35 wherein the adjusted trip delay time is determined using the function: ${\Delta \; {TripDelayTime}} = {\frac{{ActualVelocity} - {TargetVelocity}}{TargetVelocity} \times {ScalingFactor} \times {CurrentTripDelayTime}}$   And AdjustedTripDelayTime = CurrentTripDelayTime + Δ TripDelayTime 